Touch responsive user interfaces with backlit graphics are known in the art. Such user interfaces typically include a touch surface substrate that presents visual information to the user and provides an operative touch surface for the user to touch in order to actuate underlying touch sensors associated with the back side of the touch surface substrate. The touch surface substrate typically is made of glass or plastic and can be decorated to identify the locations and functions of the underlying sensors. The touch sensors typically include one or more sensor electrodes and associated control circuitry.
Alternatively, the locations and functions of the underlying touch sensors can be defined by a graphics layer associated with the back side of the touch surface substrate and one or more underlying light sources. The graphics layer typically is a substantially opaque layer having light-transmissive portions (which may be transparent or translucent) in registration with corresponding touch sensor sensing electrodes and light sources. The transparent portions of the graphics layer define indicia or other graphic elements that are visible at the touch surface when backlit by the light sources.
The light sources typically are disposed on the back surface of the printed wiring board (the surface opposite the touch surface substrate) or on a separate lighting board attached to the back surface of the printed wiring board. In order that light emanating from the light sources may reach the touch surface substrate and be visible to the user, at least the portions of the printed wiring board and touch sensor electrodes disposed in the optical path between the light source and the touch surface substrate must be substantially transparent.
One skilled in the art would know how to select such a printed wiring board and how to dispose substantially transparent sensor electrodes thereon. However, known printed wiring boards and techniques for disposing transparent touch sensor electrodes thereon have limitations. For example, the materials used to form transparent electrodes typically are expensive. Also, transparent sensor electrodes may have lesser conductivity than electrodes made of conventional, opaque materials and, therefore, may adversely affect sensor performance. Similarly, transparent wiring boards can be more expensive than opaque boards. Also, light projected through known transparent or translucent substrates typically is at least somewhat attenuated and can take on an undesirable hue. Further, light admitted into a printed wiring board may bleed laterally through the board, resulting in an undesired aura of light about the area of the touch substrate that is intended to be backlit, and reducing the light output in the area of the touch substrate that is intended to be backlit.